1. Technical Field
The present invention generally relates to an air-conditioning unit, an image forming apparatus, such as, a copier, a printer, a facsimile machine, a plotter, or a multifunction peripheral (MFP) having at least two of coping, printing, facsimile transmission, plotting, and scanning capabilities, that incorporates an air conditioner, and a method of switching an airflow channel; and more particularly, to an air-conditioning unit to adjust temperature at a specific position inside an apparatus, an image forming apparatus including the air-conditioning unit, and a method of switching an air-conditioning channel therein.
2. Description of the Background Art
Image forming apparatuses, such as printers, facsimile machines, copiers, and digital multifunction machines generally record images constituted of characters, symbols, illustrating, or combinations thereof on sheets of recording media, such as paper, overhead projector (OHP) film, and the like, according to image data. Among various types of image forming apparatuses, electrophotographic image forming apparatuses can print high-resolution images on plain paper at high speed and are widely used.
Image forming components inside electrophotographic image forming apparatuses are susceptible to environmental changes. In particular, properties thereof can change depending on temperature and humidity.
Typically, image forming apparatuses include multiple heat generators such as an optical writing device, a fixing device, a developing device, and driving motors to rotate a photoreceptor and the like. Thus, temperature can increase at various positions inside the apparatus.
Therefore, there are image forming apparatuses that include an air conditioner. FIGS. 12A and 12B illustrate a configuration and an operational theory of a typical air conditioner, a vapor-compression refrigerator.
The vapor-compression refrigerator shown in FIG. 12A includes a compressor 101 to compress coolant, a first heat exchanger (condenser) 102 to exchange heat between coolant and air, a second heat exchanger (evaporator) 103, an expansion valve 104 to depressurize coolant, and a four-way valve 105 to switch the route of coolant between multiple channels. The vapor-compression refrigerator can heat and cool air by repeating the following cycle.
1. Compression: Compress low-pressure and low-temperature vapor of coolant by the compressor 101 into high-pressure and high-temperature valor of coolant.
2. Condensation: Send the coolant vapor compressed by the compressor 101 to the first heat exchanger 102 and cool the coolant vapor with air into liquid (liquid coolant). At that time, air is heated.
3. Expansion: Depressurize the high-pressure liquid coolant liquefied by the first heat exchanger 102 by the expansion valve 104.
4. Evaporation: Cause the liquid coolant depressurized by the expansion valve 104 to evaporate using the second heat exchanger 103, and draw heat from the air. Thus, the air is cooled.
FIG. 12C is a temperature entropy diagram or T-S diagram illustrating the above-described processes.
The compressor 101 compresses dry saturated vapor A of coolant to a pressure higher than the saturated vapor pressure at a predetermined temperature in the first heat exchanger 102, thus creating superheated saturated vapor B. The superheated saturated vapor B is then sent to the first heat exchanger 102. In the first heat exchanger 102, heat is exchanged between the superheated saturated vapor B and air. Heat Q1 is drawn out from the superheated saturated vapor B, and the superheated saturated vapor B is cooled and liquefied into saturated liquid C. The saturated liquid C is sent to the expansion valve 104, and isenthalpic expansion is executed by the expansion valve 104. Thus, the saturated liquid C becomes wet vapor D and is sent to the second heat exchanger 103. The wet vapor D draws in heat or heat amount Q2 from air and vaporizes, thus returning to the dry saturated vapor A.
FIG. 12B illustrates a state in which the orientation of the four-way valve 105 is switched from that shown in FIG. 12A. More specifically, in FIG. 12A, the channel of coolant starting from the compressor 101 extends to the first heat exchanger 102, the expansion valve 104, and the second heat exchanger 103 in that order. By switching the channel of coolant shown in FIG. 12A from the compressor 101 to the second heat exchanger 103, the expansion valve 104, and the first heat exchanger 102 as shown in FIG. 12B, functions of the first and second heat exchangers 102 and 103 can be switched between a condenser and an evaporator; and an evaporator and a condenser.
However, the volume of air conditioning target can be large when air in the entire image forming apparatus is conditioned by the above-described air conditioner, resulting in increases in cost, size of the apparatus, noise, and power consumption in accordance with the control capacity. Therefore, when an air conditioner is employed in an image forming apparatus, typically power consumption is greater compared with a configuration employing a cooling fan.
Therefore, air conditioning may be performed in or around only an image forming unit including a photoreceptor, a developing device, and the like.
For example, JP-2003-122208-A proposes the following configuration to efficiently remove substances hazardous to image formation from the surroundings of the photoreceptor. The configuration includes a body case, an image forming unit including an image forming case housing at least the photoreceptor and, and an air-conditioning means to remove the hazardous substances, which flows in the image forming unit from outside. The photoreceptor is partly exposed from an opening for transfer formed in the image forming unit. The opening for transfer is the only opening from which the hazardous substances may flow in the image forming unit in the state in which the image forming unit is attached to the body case.
The air-conditioning means is disposed on the entrance side of a flow channel extending from the outside of the image forming unit via the image forming unit to the outside. Further, the air-conditioning means is positioned midway in a circulation channel through which air flows in the image forming unit after discharged from the image forming unit to the outside.
Additionally, JP-3924484-B (JP-2003-280472-A) proposes a configuration to maintain satisfactory performance of a cleaning blade to scrape off residual toner from the photoreceptor even in the case where temperature and humidity around the electrophotographic image forming apparatus change. The apparatus includes a temperature adjusting device having heating capability to supply heated air and cooling capability to supply cooled air, an air-conditioning means to adjust temperature of the cleaning blade, a temperature sensor to measure temperature of the cleaning blade, and a temperature control means to drive the air-conditioning means to set the temperature of the cleaning blade at a temperature suitable to scrape off residual toner according to detection of the temperature sensor and a preset reference temperature. This image forming apparatus includes multiple image forming modules to form different color images, and each image forming module includes at least the photoreceptor, the developing unit, and the cleaning unit housed in a common case. Each case defines a substantially closed space in which temperature is controlled by the air-conditioning means, and the preset reference temperature is set for each of the multiple image forming modules.
JP-3924484-B (JP-2003-280472-A) further proposes a configuration that employs a humidity controlling means, instead of or in addition to the temperature adjusting device, and a reference humidity is set instead of the reference temperature.
There are two air-conditioning types to control temperature and humidity inside image forming apparatuses (apparatus bodies, in particular). In one type of air conditioning, airflow generated by the air conditioner (hereinafter also “conditioning airflow” or “flow of conditioning air”) is supplied to a conditioning target inside the apparatus body and then is again sucked in by the air conditioner (hereinafter “circulation type”). In another type of air conditioning, the airflow generated by the air conditioner is supplied to the conditioning target inside the apparatus body and exhausted outside the image forming apparatus. The air conditioner sucks in fresh external air outside the image forming apparatus (hereinafter “intake and exhaust type”). To keep the conditioning target at a target temperature, in either of the above-described air-conditioning types, flow of conditioned air at a predetermined temperature is generated, and the predetermined temperature is set according to the target temperature.
When the environmental temperature outside the apparatus body is higher than that of the conditioning airflow, temperature of the airflow that has passed through the conditioning target may be lower than the temperature outside the apparatus body. Under such conditions, the airflow at the predetermined temperature can be generated with a smaller amount of energy in the circulation type air conditioning since the temperature of air sucked in by the air conditioner is lower compared with the intake and exhaust type.
By contrast, when the temperature outside the apparatus body is lower than that of the conditioning airflow, temperature of the airflow that has passed through the conditioning target may be higher than the temperature outside the apparatus body. Under such conditions, the airflow at the predetermined temperature can be generated with a smaller amount of energy in the intake and exhaust type air conditioning since the temperature of air sucked in by the air conditioner is lower compared with the circulation type.
Thus, from the viewpoint of energy consumption, in some cases, one of the circulation type and the intake and exhaust type is advantageous over the other depending on the temperature outside the apparatus body.
In view of the foregoing, the inventors of the present invention recognize there is a need for generating air conditioning airflow in an energy-efficient method regardless of the temperature outside the apparatus body.